in-band: use open_type when opening internal device

in-band: use open_type when opening internal device

in-band code will open a device that it expects to be the main internal port of
the bridge. However, it's possible that the correct type is a different one. For
dpif-netdev, it might be a tap device, or a dummy device for dummy datapaths.
ofproto_port_open_type will give the correct type.

While this doesn't cause any problems right now, as the needed type would be
opened already, a later patch assumes netdev with different types cannot be
opened.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>